1. Field of the Invention
The present invention relates generally to location-based services in wireless telecommunication networks and, more specifically, to providing GPS assistance data to roaming user equipment.
2. Description of the Related Art
It is desirable to be able to determine the geographic location of a cellular telephone or other mobile user equipment (UE) in a wireless telecommunication network. The earliest use of UE location information related to emergency calling (e.g., the E911 system used in the United States), in which the network determines the location of a caller's UE and routes the call to the nearest Public Service Access Point for handling by an emergency operator. Location-based services are now expanding far beyond emergency calling, to such diverse uses as navigation, mapping, tracking and gaming.
One method by which UE location can be determined is known as Assisted GPS (A-GPS). In A-GPS, the wireless telecommunication network transmits “assistance data” to the UE to aid the UE in finding and utilizing signals transmitted by the Global Positioning System of satellites, as the GPS satellite signals that reach the receiver are sometimes weak or cannot be detected at all due to shielding and reflection from buildings or terrain. Various third parties maintain databases that provide information on the locations of GPS satellites. The databases relate geographic locations to sets of assistance data. A wireless telecommunication service provider can use the database to obtain the assistance data to transmit to a subscriber's UE when the UE location is needed.
A UE indicates that it needs assistance data by transmitting an assistance data request. The request includes information relating to the location of the UE within the service provider's network or, if the UE is roaming, the foreign network, including a Mobile Network Code (MNC) identifying the service provider on whose network the UE is operating, a Mobile Country Code (MCC) identifying the country in which the UE is operating, a Location Area Code identifying the region or area in which the UE is operating, and a Cell ID identifying the cell in which the UE is operating. By identifying the cell in which the UE is operating, the network can use the corresponding geographic location of that cell to retrieve the corresponding set of assistance data from the database. An underlying assumption is that the network that acts upon the assistance data request can determine the geographic location of the cell in which the UE is operating.
There are two major approaches that wireless telecommunication networks use to provide location-based services: control plane and user plane. The control plane approach sends GPS assistance data on the control channels that are inherent (as defined by the applicable standards) in a service provider's network infrastructure. The user plane approach sends GPS assistance data via same channels that carry user data or voice communications, typically in Internet Protocol or Short Messaging Service format. The control plane approach was originally devised for implementing emergency (E911) calling and is well suited for location-based services (LBS) in which an application or other element in the service provider network needs to determine UE location without user intervention. The user plane approach is generally believed to be better suited for LBS applications (or applets) running locally on the UE and operated by a user. With LBS applications expanding far beyond emergency calling into highly interactive areas such as navigation, mapping, tracking and gaming, network service providers are increasingly adopting the user plane approach. A standard that has emerged for implementing the user plane approach is known as Secure User Plane Location (SUPL).
The SUPL standard is directed to enabling LBS applications to be run on any A-GPS-capable phone or other UE on any wireless telecommunication network. Nevertheless, one deficiency of SUPL is that, when a subscriber's UE is roaming and requests assistance data, it is expected that the subscriber's home network SUPL server will provide it. The home network typically does not have a comprehensive database relating the identity of every cell (Cell ID) of all of its worldwide roaming partners' networks to its geographic location and thus to the set of assistance data corresponding to that location. The home network may have such a Cell ID database that includes the locations of some of its roaming partners' cells, but maintaining a current database of all of its worldwide roaming partners' cells would require extreme cooperation and frequent exchange of information among network service providers. One problem in maintaining a current database is that service providers “re-home” cells from time to time, i.e., shift the location of a cell site, or renumber Cell IDs. It has been suggested to create a network in which the SUPL servers of different service providers communicate with each other or communicate with a centralized worldwide Cell ID database, but even if such a system were available it may suffer from other problems and deficiencies.
It would be desirable to provide a method and system for providing A-GPS assistance data to roaming UE without a comprehensive Cell ID database that includes all roaming partners. It is to the provision of such a method and system that the present invention is directed.